Natural killer (NK) cells are an important effector cell type for adoptive cancer immunotherapy. Similar to T cells, NK cells can be modified to express chimeric antigen receptors (CARs) to enhance antitumor activity.
Successful application of CAR-modified T cells in patients with CD19-positive malignancies has demonstrated the potency of this approach for adoptive cancer immunotherapy (see e.g. Grupp et al., 2013), and CAR T cells targeting a variety of different tumor antigens are under active clinical development (Kalos et al., 2013). CAR-mediated retargeting of natural killer (NK) cells has been attempted less frequently, and so far no clinical data for such an approach are available. NK cells play an important role in cancer immunosurveillance, and represent an important effector cell type for adoptive cancer immunotherapy (Geller and Miller, 2011). In contrast to T cells, they do not require prior sensitization and recognition of peptide antigens presented in complex with MHC molecules. Instead, their cytotoxicity can be triggered rapidly upon appropriate stimulation through germline-encoded cell surface receptors (Koch et al., 2013), that in part signal through CD3ζ. Hence, CD3ζ-containing CARs readily link to endogenous signaling pathways in NK cells and trigger cytolytic activity (see e.g. Müller et al., 2008). Despite these advances, experience with CAR-engineered NK cells and their clinical development is still limited. Due to efficient antiviral defense mechanisms, gene transfer into NK cells with retro- and lentiviral vectors as well as physical transfection methods are less efficient than in T cells, complicating the generation of large numbers of CAR-expressing cells (Boissel et al., 2009). This restriction can be overcome by employing clinically applicable NK cell lines such as NK-92, which allow isolation and expansion of CAR-expressing cells from a bulk of untransduced cells (Müller et al., 2008).
Phase I studies in cancer patients demonstrated the safety of infusion of unmodified NK-92 cells, which were irradiated prior to application to prevent permanent engraftment. Thereby clinical signs of activity were only observed in a subset of patients (Tone et al., 2013), likely due to insufficient tumor recognition by the unmodified NK-92 cells which lack a tumor-specific receptor.
The present invention aims to provide improved CAR-engineered NK cells, which are suitable for clinical use, in particular in the treatment of cancers and as targeted cell therapeutic agents.
It is a further objective of the present invention to provide means and methods for generating and molecularly identifying improved CAR-engineered NK cells.